The obtaining of samples of fish larvae in rivers and other bodies of water is required for determining the condition of the river with respect to pollution, and environmental impact of electric generating stations and other equipment located along the river, and that require large quantities of water for use in their cooling apparatus.
The term "larvae" is used herein to designate fish life in its early stages, including egg, young fish with a yolk sac, and shortly thereafter, these being the times when the fish life is most delicate and likely to be destroyed by mechanical impact such as abrasion along a mesh seine and impact when passing through a pump.
The invention will be described as used for sampling water before and after it passes through the cooling equipment of a power plant, but it can be used for sampling measured quantities of river water (lakes and other bodies of water being considered the equivalent of rivers for purposes of this invention) to determine the concentration of the marine life at selected locations in the river.
In the past, conical nets of fine mesh, through which the samples of fish life did not pass, were dragged through the water to collect samples. The abrasion of the mesh against the larvae caused mechanical injury, and many of the samples were killed. Counts made were unreliable because there was no way of determining the number of larvae killed by the mesh and the number of dead larvae in the water before coming into contact with the mesh. Moving the conical net through the water at higher velocity resulted in destruction of greater numbers of the larvae.
Larger area screens, of fine mesh, were used in chambers where the velocity of the water could be made low as the result of the increase in net area; but pumps supplying the water to the chambers caused agitation fatal to some of the larvae and injurious to other parts of the sample. Even the use of recessed impellers for the pumps was insufficient to prevent injury to the samples by abrasion and impact.
This invention passes water through fine mesh partitions of large area and with resulting low water velocity; and preferably with two-stage separation to obtain more concentrated larvae in the samples of water collected. No pump is used until the larvae have been removed from the water; that is, the water is not pumped until after it has been passed through the mesh partition.
The preferred embodiment has the mesh partition in chambers that are at least partially submerged in the water from which the sample is to be taken, and the water flows into the chamber by gravity. Pumps beyond the chambers that have the mesh partitions are preferably carried by a support having no stiff connection with the chambers, and thus vibration of the pump and pump motors cannot reach the water samples. Flexible hoses connect the chambers, downstream of the mesh partitions, with the pumps.
Other objects, features and advantages of the invention will appear or be pointed out as the specification proceeds.